JP6452110B2 - Hand-held probe - Google Patents

Description

  The present invention relates to a hand-held probe.

  Photoacoustic imaging (PAI) is known as a technique for imaging a light absorber (for example, a blood vessel inside a living body) in a subject. Photoacoustic imaging is a technique that uses the fact that a photoacoustic wave is generated from a light absorber due to a photoacoustic effect when light is irradiated on an object, and converts the distribution of the light absorber into image data. For example, blood vessels in a living body can be imaged by using hemoglobin as a light absorber.

  On the other hand, ultrasonic imaging is known as a method for rendering structural information in a subject. In ultrasonic imaging, ultrasonic waves are transmitted to a subject from many detection elements (transducers) arranged on the probe. Then, image data is generated by receiving a reflected wave generated at the acoustic impedance interface in the subject.

  Non-Patent Document 1 describes a technique for acquiring an image obtained by photoacoustic imaging and an image obtained by ultrasonic imaging using the same handheld probe.

JJ Niederhauser, M. Jaeger, R. Lemor, P. Weber, and M. Frenz, “Combined ultrasound and optoacoustic system for real-time high-contrast vascular imaging in vivo,” IEEE Trans. Med. Imaging 24, 436-440 (2005)

  Generally, the photoacoustic probe has a circuit configuration dedicated to reception, and it is necessary to add an ultrasonic transmission circuit in order to use it for ultrasonic imaging. However, this increases manufacturing costs. In addition, noise may be generated by a switch circuit for switching between transmission and reception. Further, since the detection element has transmission characteristics, reception characteristics may be deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a hand-held probe suitable for photoacoustic imaging and ultrasonic imaging and having a simple configuration.

The present invention employs the following configuration. That is,
A gripping part;
A plurality of detection elements that receive acoustic waves and output electrical signals;
A detection surface on which the plurality of detection elements are arranged;
A light absorber support part in which a light absorber that absorbs light emitted from a light source and generates an acoustic wave is disposed;
It is a hand-held probe characterized by having.

  According to the present invention, a hand-held probe suitable for photoacoustic imaging and ultrasonic imaging and having a simple configuration can be provided.

FIG. 3 is a diagram illustrating a configuration example of a handheld probe according to the first embodiment. FIG. 3 is a cross-sectional view of the handheld probe according to the first embodiment. FIG. 3 is a diagram illustrating a processing flow according to the first embodiment. The figure which shows the mode of the received signal of Embodiment 1. FIG. FIG. 6 is a diagram illustrating a configuration example of a cover member according to a second embodiment. FIG. 6 is a diagram illustrating a hand-held probe according to a third embodiment. The block diagram which showed the structure of the subject information acquisition apparatus.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described below should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. Therefore, the scope of the present invention is not intended to be limited to the following description.

  The present invention relates to a technique for detecting acoustic waves propagating from a subject, generating characteristic information inside the subject, and acquiring the characteristic information. Therefore, the present invention can be understood as a subject information acquisition apparatus or a control method thereof, a subject information acquisition method, or a signal processing method. The present invention can also be understood as a program that causes an information processing apparatus including hardware resources such as a CPU to execute these methods, and a storage medium that stores the program.

  The subject information acquisition apparatus of the present invention irradiates a subject with light (electromagnetic waves) and receives (detects) an acoustic wave generated and propagated at a specific position in the subject or on the subject surface according to the photoacoustic effect. Includes equipment using photoacoustic tomography technology. Such an object information acquiring apparatus can also be called a photoacoustic imaging apparatus because it obtains characteristic information inside the object in the form of image data or the like based on photoacoustic measurement.

  The subject information acquisition apparatus of the present invention transmits an acoustic wave to a subject, receives a reflected wave (echo wave) reflected inside the subject, and obtains subject information as image data. Includes devices that use.

  The characteristic information in the photoacoustic device is the distribution of the source of acoustic waves generated by light irradiation, the initial sound pressure distribution in the subject, or the optical energy absorption density distribution, absorption coefficient distribution, and tissue derived from the initial sound pressure distribution. The concentration distribution of the constituent substances is shown. Specifically, it is a blood component distribution such as an oxygenated / reduced hemoglobin concentration distribution, an oxygen saturation distribution obtained therefrom, or a distribution of fat, collagen, and water. Further, the characteristic information may be obtained as distribution information of each position in the subject, not as numerical data. That is, distribution information such as an absorption coefficient distribution and an oxygen saturation distribution may be used as the subject information. The characteristic information derived from the photoacoustic wave can also be called function information indicating a difference in function due to the substance inside the subject.

  The characteristic information acquired by the ultrasonic echo device is information reflecting the difference in acoustic impedance of the tissue inside the subject. The characteristic information derived from the ultrasonic echo can also be called morphological information reflecting the structure inside the subject.

  The acoustic wave referred to in the present invention is typically an ultrasonic wave and includes an elastic wave called a sound wave or an acoustic wave. An acoustic wave generated by the photoacoustic effect is called a photoacoustic wave or an optical ultrasonic wave. An electric signal converted from an acoustic wave by a probe or the like is also called an acoustic signal.

[Embodiment 1]
Next, Embodiment 1 of the present invention will be described with reference to the drawings. In the following description, unless otherwise specified, “photoacoustic wave” refers to a photoacoustic wave generated from a light absorber inside or on the surface of a subject. On the other hand, the photoacoustic wave generated from the light absorber disposed on the probe is called “transmitted ultrasonic wave”. When it is necessary to clarify the distinction between the two, they are also called “subject-derived photoacoustic waves” and “probe-derived photoacoustic waves”, respectively. In addition, an echo wave in which the transmitted ultrasonic wave is reflected on the subject surface or inside is called an “ultrasonic echo”. However, these names are for facilitating the distinction and are not intended to limit the wavelength of each elastic wave.

<Configuration of probe>
FIG. 1 is a diagram illustrating a configuration example of a hand-held (hand-held) probe according to the present embodiment. The hand-held probe 1 has a cylindrical holding part 2 for an operator to hold. The grip portion 2 also functions as a housing that holds various components. The grip 2 is not limited to a cylindrical shape. For example, an elliptical column shape or a rectangular column shape may be used, and unevenness may be provided so that the operator can easily grasp the shape.

  The detection surface 3 is a surface that intersects the central axis 5 of the grip portion 2. A plurality of detection elements 4 (transducers) are provided on the detection surface 3. The hand-held probe 1 of FIG. 1 can irradiate a subject with light guided by an optical system 6 from a light source (not shown) from an emission end 6 a disposed substantially at the center of the detection surface 3.

  In FIG. 1, the detection surface 3 is a curved surface that is recessed with respect to the subject. By making the detection surface 3 a curved surface, it is possible to obtain an effect that the measurement target of ultrasonic imaging can be focused on the region of interest in the subject. As the curved surface, a shape of a part of an ellipsoid is preferable, and a spherical crown shape is more preferable. However, the detection surface 3 may be a flat surface. The hand-held probe 1 is pressed against the subject so that the detection surface 3 faces the subject.

  The plurality of detection elements 4 receive photoacoustic waves and ultrasonic echoes that propagate from the subject, convert them into electrical signals, and output them. The arrangement method of the plurality of detection elements 4 is not particularly limited. For example, various arrangement methods such as a square lattice shape, a rectangle, a pentagon or more polygon, a circle, an ellipse, a sector, and a concentric circle can be used. The arrangement of the detection elements 4 may be a concentric ring. As a result, the symmetry of the element arrangement is increased and a good reconstructed image can be obtained. At that time, the elements are preferably arranged concentrically around the light emitting end.

  As the detection element 4, a piezoelectric element, cMUT (Capacitive micromachined ultrasonic transducers), PVDF (PolyVinylline DiFluoride), a Fabry-Perot sensor, or the like can be used. The element size and the arrangement interval may be determined from the viewpoint of reception sensitivity and directivity according to the application.

  It is preferable to cover 70% or more of the detection surface 3 by the plurality of detection elements 4 arranged on the detection surface 3, and it is preferable to cover 85% or more of the detection surface 3. Accordingly, photoacoustic waves and ultrasonic echoes propagating from the subject can be efficiently received from various angles, and highly accurate image data can be generated.

  Each detection element 4 preferably has an equal solid angle with respect to the region of interest. Therefore, it is desirable that the detection elements 4 are arranged in an equally distributed manner, such as a spiral arrangement or a Fibonacci arrangement. Further, in order to increase the number of arrangement of the detection elements 4 and increase the SNR, it is desirable to arrange the detection elements 4 concentrically with respect to the emission end 6a.

A pulse laser device is suitable as a light source (not shown). As the laser light, light having a wavelength at which the light absorber in the subject has absorption characteristics is preferable. For example, near infrared light is suitable for hemoglobin in blood. Further, by using a wavelength tunable laser that generates light of a plurality of wavelengths, detailed information such as oxygen saturation can be acquired. However, a flash lamp or LED can be used instead of the laser device.

  As the optical system 6 that propagates light from the light source, various optical members such as a fiber bundle, a mirror, a prism, and a waveguide can be used. Then, the propagated light is irradiated to the subject from the emission end 6a such as the end of the fiber bundle.

  As will be described in detail later, a cover member 7 is provided on the side of the hand-held probe 1 that contacts the subject. The light absorber 8 in the figure is disposed on the cover member 7. That is, in this embodiment, a cover member functions as a light absorber support part. When the detection surface 3 of the hand-held probe 1 is pressed against the subject, the cover member is positioned between the subject and the detection surface.

  FIG. 2 is a cross-sectional view of the hand-held probe 1 in a state of being in contact with the subject. In the present embodiment, since the detection surface 3 is concave, a gap is formed when the casing is pressed against the subject 10. The cover member 7 is a member that contacts the subject 10 at that time. In other words, a sealed space is formed between the cover member 7 and the detection surface 3 on which the detection element 4 is provided.

  This sealed space is filled with a coupling agent 9 for acoustically matching the detection element 4 and the subject 10. As the coupling agent 9, one having an acoustic impedance close to that of the subject 10 is suitable. For example, water or castor oil can be suitably used as the coupling agent 9. As the coupling agent 9, one having a high transmittance with respect to the irradiation light is used in order to propagate the light to the subject 10.

  The cover member 7 preferably has flexibility so as not to hinder the propagation of photoacoustic waves and ultrasonic echoes. For example, a flexible film-like member such as rubber is preferable. Further, in order to propagate the irradiation light to the subject 10, a light transmissive material is used. When the cover member 7 is filled with the coupling agent 9, the detection element and the subject are acoustically matched. The cover member 7 also prevents direct contact between the subject 10 and the coupling agent 9. In FIG. 2, when the cover member 7 filled with the coupling agent is pressed against the subject 10, the cover member 7 is deformed along the shape of the subject 10 and is in close contact with the subject 10.

  A coupling agent may be further applied between the subject 10 and the cover member 7. As a result, adhesion and acoustic consistency between the subject 10 and the cover member 7 are enhanced. Furthermore, the relative movement of the probe 1 with respect to the subject 10 becomes smooth during measurement. The cover member 7 may be configured to be detachable from the probe 1 as a bag-shaped member. It is useful in terms of hygiene to replace the bag-like cover member 7 filled with the coupling agent in advance for each measurement or for each subject, for example.

  Even when the detection surface 3 is planar, a cover member enclosing a coupling agent may be provided from the viewpoints of protection of the detection element, improvement in acoustic impedance matching, improvement in the comfort of the subject, and the like. preferable.

<Light absorber>
The cover member 7 has a dot-shaped light absorber 8. When a part of the light from the emission end 6a is irradiated on the light absorber 8, the transmission ultrasonic wave S101 is generated by the photoacoustic effect. This transmitted ultrasonic wave reaches the subject 10 and is reflected by the region of interest 10a or the like to become an ultrasonic echo S103. By receiving this with the detection element, ultrasonic imaging is realized. On the other hand, the remaining irradiation light reaches the subject and generates a photoacoustic wave. Photoacoustic imaging is realized by the detection element receiving this. Thus, ultrasonic imaging and photoacoustic imaging can be performed with a single probe that has a simple configuration and does not have an ultrasonic transmission function.

  From the viewpoint of efficiently generating transmission ultrasonic waves, the light absorber 8 is preferably disposed on the central axis 5 (on the optical axis) with high light intensity. The dot size of the light absorber 8 affects the frequency of transmitted ultrasonic waves. Therefore, it is preferable to determine the dot size of the absorber so that the frequency of the transmitted ultrasonic wave is within the band sensitivity of the detection element 4. As an example of the dot size, when the cover member 7 has a thickness of 500 μm, the dot of the light absorber 8 has a diameter of about 400 μm. Thereby, unevenness with respect to the subject surface can be reduced.

  As the material of the light absorber 8, for example, a material that efficiently generates transmission ultrasonic waves such as a material containing carbon is used. Further, if the light absorber 8 completely absorbs light, the photoacoustic imaging is affected. Therefore, the size and material of the light absorber 8 are determined so that part of the light avoids or passes through the light absorber 8 and reaches the subject 10. As an example, consider a case where a light irradiation region has a diameter of 15 mm in a hand-held probe having a detection surface 3 having a diameter of about 500 mm. If the light absorber 8 having a diameter of about 400 μm as described above is used with this probe, most of the irradiation light can reach the subject, so that it hardly affects the photoacoustic imaging.

  When the position of the light absorber 8 is greatly deviated from the central axis 5 due to contact with the subject, the signal intensity of the transmitted ultrasonic wave is lowered. Therefore, when creating the cover member 7, it is preferable to use a partially hard material only in the vicinity of the grip portion 2. In order to cope with such a positional shift, a configuration in which a plurality of dots are arranged on the cover member and at least one of the dots exists on the optical axis is also conceivable. However, when there are a plurality of dots, it is difficult to determine which dot the acquired ultrasonic echo is derived from. Therefore, it is more preferable to arrange only one dot.

  Further, when the cover member 7 can be replaced as described above, a plurality of cover members having different materials, sizes, numbers, positions, and the like of the light absorber may be prepared and replaced according to the measurement contents. Moreover, the cover member 7 is good also as a structure which has inlets like a valve. As a result, the coupling agent can be filled between the cover member 7 and the detection surface via the injection port only at the time of measurement. As a result, leakage of the coupling agent due to breakage of the cover member 7 during storage or transportation can be prevented. The inlet is preferably provided at the edge of the detection surface so as not to hinder measurement.

<Processing flow>
Next, a measurement sequence according to the present embodiment will be described with reference to FIG. FIG. 3A shows a main processing flow. FIG. 3B is a detailed description of step S302, and FIG. 3C is a detailed description of step S305.

(Step S301: Preparation for measurement)
In this step, settings are made such as starting up the apparatus, attaching the cover member 7 to the hand-held probe 1, and applying an ultrasonic gel to the probe to contact the subject. Thereby, it will be in the state which can be measured as shown to the schematic diagram of FIG. In this example, a region of interest (ROI) 10a in the subject 10 is a measurement target.

(Step S302: Light irradiation)
In step S3021, the light transmitted from the optical system 6 after being irradiated from the light source is irradiated from the emission end 6a. In step S3022, the light absorber disposed on the cover member 7 absorbs light, thereby generating a probe-derived photoacoustic wave (transmission ultrasonic wave) S101. A part of the transmitted ultrasonic wave is received by the detection element 4 via the coupling agent 9. Another part of the transmitted ultrasonic wave is reflected by an acoustic impedance interface such as a structure inside the region of interest 10a or the surface of the subject to become an ultrasonic echo S103, which is received by the detection element 4. The light irradiation process may be repeated a plurality of times.

  Further, the subject-derived photoacoustic wave S102 is generated by the light absorber of the region of interest 10a absorbing the light. The photoacoustic wave is received by the detection element 4 via the region in the subject and the coupling agent 9.

(Step S303: Acoustic wave reception)
FIG. 4 shows a representative example of an electrical signal based on the acoustic wave detected by the detection element 4. The horizontal axis represents the elapsed time after light irradiation. The electrical signal is determined according to the length of the path through which the acoustic wave has passed after generation and the sound speed of the area through which the acoustic wave has passed. The vertical axis represents the strength of the electrical signal.

  In FIG. 4, first, a signal having a high intensity is observed. This corresponds to the transmission ultrasonic wave S101 derived from the light absorber 8 arranged in the cover member. The next observed signal corresponds to the photoacoustic wave S102 generated from the light absorber in the region of interest. The next observed signal corresponds to the ultrasound echo S103, where the transmitted ultrasound S101 is reflected by a structure in the region of interest.

  To be precise, the photoacoustic wave S102 generated from the region of interest is also reflected by the structure. However, since the energy generated by this reflected wave is small, the signal intensity is small and is generally ignored or not observed. At this time, if the size of the region of interest is small relative to the distance from the dot-shaped light absorber disposed in the cover member, the signals are not observed at the same time.

(Step S304: signal processing)
In this step, signal processing according to need is performed on the electrical signals output from each detection element. For example, amplification processing, digitization processing for an analog electric signal, gain processing according to the path length and light amount of acoustic waves, correction processing of element characteristics, and the like can be given.

(Step S305: Image reconstruction)
In this step, photoacoustic imaging processing using photoacoustic waves and ultrasonic imaging processing using ultrasonic echoes are performed. Various known techniques can be used for image reconstruction in steps S3051 and S3053. The processing in this step is not limited to the flow shown in FIG. 3C, and an ultrasonic image and a photoacoustic image may be generated in parallel.

このとき投影データに相当する項ｂ（ｒ_０，ｔ）を、式（２）に示す。

A back projection algorithm in a three-dimensional space can be applied to the reconstruction of the photoacoustic wave. For example, in the case of the UBP method (Universal Back-Projection), the initial sound pressure distribution p ₀ (r) is estimated in time space by the following equation (1).

At this time, the term b (r ₀ , t) corresponding to the projection data is shown in Expression (2).

ここで、ｐ（ｒ）はＳ１００で取得した光音響波信号、ｒは各検出素子の位置、ｔは時間であり、θは受信器と任意のデータ領域とがなす角度である。 Further, the solid angle term dΩ ₀ of the receiver for an arbitrary data region is expressed by Equation (3).

Here, p (r) is the photoacoustic wave signal acquired in S100, r is the position of each detection element, t is time, and θ is the angle formed by the receiver and an arbitrary data area.

In addition, when the distance between the sound source and the measurement position is sufficiently larger than the size of the sound source, the projection data term b (r ₀ , t) may be expressed by the equation (4).

ここでτは、膜内の光吸収体から投影位置ボクセルまでの距離と、i番目の検出素子か
らの投影位置ボクセルまでの距離の和を音響伝搬速度で割ることで求まる遅延時間となる。
ωは窓関数などの重みファクターなどであり検出素子の指向性や再構成画像の所望の解像度やＳＮに応じて変更される。 Since the cover member 7 is deformed by contact with the subject, the position of the light absorber 8 provided on the cover member 7 may be changed as compared with the case where the cover member 7 is not in contact with the subject. Therefore, the influence of the displacement of the light absorber 8 on the signal may be corrected. In step 3052, the position information of the light absorber can be acquired based on the photoacoustic wave S <b> 101 that directly enters the detection element from the light absorber 8. In step S3053, the back projection algorithm was applied in the three-dimensional space as well as the photoacoustic image when calculating the image reconstruction I (r) of the reflected ultrasound (formula (5)).

Here, τ is a delay time obtained by dividing the sum of the distance from the light absorber in the film to the projection position voxel and the distance from the i-th detection element to the projection position voxel by the acoustic propagation velocity.
ω is a weight factor such as a window function, and is changed according to the directivity of the detection element, the desired resolution of the reconstructed image, and SN.

  At this time, as projection data taking into account the displacement inside the subject, sampling data Si having the same phase with respect to the projection position voxel can be extracted from the time-series signals received by the detection elements, and summed to obtain an image. .

(Step S306: Image display)
Ultrasonic image data and photoacoustic image data generated by image reconstruction are displayed on a display device such as a liquid crystal display. As a display method, any method may be used such as displaying both images in a superimposed manner, displaying them side by side, or displaying them alternately. However, the effect of the present invention can be obtained even if the image is stored as image data without being displayed. Furthermore, components derived from the light absorber of the cover member are included even in the RAW data output from the detection element before the image reconstruction and the electric signal in a state where only the correction processing is performed. Therefore, the effect of the present invention can be obtained.

  As described above, according to the present embodiment, ultrasonic imaging and photoacoustic imaging can be performed with a simple probe including only a single detection element that does not have an ultrasonic transmission function. Therefore, in the diagnosis using a plurality of modalities, it is possible to expect a cost reduction, an improvement in operating rate, and an easy maintenance.

[Modification]
When a flexible material is used as the cover member 7, the position of the light absorber on the cover changes depending on the strength and direction when the probe is pressed against the subject. As a result, the positional relationship between the light absorber serving as the sound source and the subject changes, and the transmission ultrasonic wave arrival time from the sound source to the subject and the arrival time of the ultrasonic echo to the detection element change. Then, the position where the component derived from the reflected wave from the region of interest is shifted in the digitized electric signal, which may affect the accuracy of reconstruction.

  In addition, as the distance between the sound source and the region of interest increases, the degree of attenuation of the transmitted ultrasonic wave increases, which may affect the S / N ratio of the reconstructed image. Furthermore, the intensity of the transmitted ultrasonic wave decreases as the distance between the light emitting end and the light absorber increases due to the attenuation of the irradiation light, which may affect the S / N ratio of the reconstructed image.

  Here, if the change in the position of the light absorber due to the deformation of the cover member can be grasped, the position in the digital signal of the signal component derived from the reflected wave propagated from the region of interest can be known, and appropriate reconstruction can be performed. In addition, correction such as gain processing can be performed for the attenuation of the transmission acoustic wave itself and the decrease of the transmission ultrasonic wave intensity corresponding to the attenuation of the irradiation light. Therefore, in this modification, a method for grasping the position of the light absorber in advance in a state where the probe is pressed against the subject (contact state) will be described.

  First, the user performs preliminary light irradiation in a contact state. As a result, photoacoustic waves are generated not only from the light absorber in the cover member but also from the light absorber in the subject, but they can be identified because they have different detection times and intensities. Then, image reconstruction is performed using an electrical signal derived from the light absorber in the cover member. As a result, the position information of the light absorber can be acquired.

  According to this modification, it is possible to grasp the position of the light absorber disposed on the cover member and realize appropriate image reconstruction. In this modification, the light irradiation for obtaining position information and the light irradiation for image reconstruction are not necessarily performed separately. That is, after acquiring the electrical signal as shown in FIG. 4, first, the position of the light absorber is grasped by image reconstruction using the portion of S101, and S102 (corresponding to the subject-derived photoacoustic wave) and S103 ( It may be used for image reconstruction (corresponding to ultrasonic echo).

  As another modification, a configuration in which the light emission end is not included in the housing of the gripping unit is also conceivable. In this case, an optical member that emits light is required in addition to the probe, but the degree of freedom in the positional relationship between the light irradiation position and the light absorber increases.

As another modification, a configuration in which the cover member is a bag-like member is also conceivable. When the matching agent is sealed in a region defined by the detection surface and the film-like cover member, it may be necessary to waterproof the detection element 4. However, it is possible to reduce the necessity of applying a waterproof treatment to the detection element 4 by using the cover member as a bag-shaped member. Also in this case, the bag-shaped cover member can be configured to be detachable from the grip portion. Also in the case of a bag-like cover member, an injection port for injecting the matching agent may be provided.

[Embodiment 2]
In the first embodiment, only one dot of the light absorber is provided on the cover member. In this case, if there is a region within the subject in which the transmission ultrasonic wave generated from the light absorber is difficult to reach, the accuracy of the reconstructed image of the region is lowered. Such a decrease can occur when the position of the light absorber is away from the region of interest, or when the transmitted ultrasonic wave has a frequency that tends to attenuate. Therefore, in the present embodiment, a plurality of light absorber dots having different absorption wavelength peaks are arranged on the cover member 7.

  FIG. 5 shows a state where the cover member 7 of the present embodiment is viewed from the subject side. The cover member 7 includes a light absorber 1 (8a), a light absorber 2 (8b), a light absorber 3 (8c), a light absorber 4 (8d), and a light absorber 5 (8e) having different light absorption characteristics. ) Is arranged. The arrangement position of each light absorber is preferably within a range in which light from the emission end strikes. In FIG. 5, the emission end and the detection element existing on the opposite side across the cover member are omitted.

  In this embodiment, a wavelength tunable laser device is used as the light source. Then, for each pulse or time unit, light having a wavelength suitable for each of the light absorbers is irradiated to generate a transmission ultrasonic wave (probe-derived photoacoustic wave), and an ultrasonic echo is detected. As a result, five types of received signals having different sound source positions are obtained. Thereafter, an image with a high S / N ratio is obtained by averaging the acoustic signals stored in the memory or averaging the reconstructed images generated from the respective acoustic signals.

  Note that the subject-derived photoacoustic signals included in the above five types of received signals are caused by irradiation light having different wavelengths, and the type of signal can be identified from the spectrum information. Therefore, by using these signals, highly accurate photoacoustic imaging can be executed. For example, an oxygen saturation distribution image can be acquired with high accuracy if light of a wavelength that is easily absorbed by each of oxyhemoglobin and reduced hemoglobin is included in five types of light.

  According to the present embodiment, photoacoustic imaging and ultrasonic imaging can be realized over a wide area inside the subject by using a single probe with a simple configuration. In FIG. 5, five types of light absorbers indicated by reference numerals 8 a to 8 e are provided, but the number and arrangement are not limited thereto.

[Embodiment 3]
In each of the embodiments described above, the matching agent is sealed in the cover member 7. On the other hand, the probe of the present embodiment uses a gel member 11 that is a medium having acoustic impedance close to that of soft biological tissue and transmitting irradiation light. Thereby, reflection and loss of acoustic waves between the detection element and the subject can be reduced.

  FIG. 6A is a cross-sectional view showing the configuration of the hand-held probe 1 according to this embodiment. One side of the gel member 11 has a shape along the curved surface of the detection surface 3 so that air does not enter. On the other hand, the side in contact with the subject 10 has a shape suitable for the subject surface. Further, if the gel member can be removed, it is possible to replace each subject and it is hygienic. Further, a sheet-like light absorber 12 having a curvature substantially equal to that of the detection surface 3 is disposed on the center line 5 of the optical path inside the gel member 11. That is, in this embodiment, a gel member functions as a light absorber support part.

FIG. 6B shows a state where the gel member 11 is viewed from the subject side. In order to efficiently generate transmission ultrasonic waves, the sheet-like light absorber 12 is disposed so as to cover the optical axis. Therefore, when determining the material, thickness, size, etc. of the sheet-like light absorber 12, it is designed not to absorb all of the irradiation light but to transmit part of it to the subject. The sheet-like light absorber is also required to be permeable to acoustic waves. For example, a thin film of gold, silver or aluminum can be used as the material of the sheet-like light absorber.

  Among the photoacoustic waves generated in the sheet-shaped light absorber 12, the propagated wave (transmission ultrasonic wave) traveling to the side opposite to the detection element propagates to the center of curvature of the sheet-shaped light absorber 12. Accordingly, if the center of curvature of the detection surface 3 and the center of curvature of the sheet-like light absorber 12 coincide, the transmitted ultrasonic wave propagates so as to converge toward the center of curvature. As a result, a strong signal amplitude is formed at the center of curvature, and highly accurate image data is obtained. In addition, since the reception focus of the photoacoustic wave is at the center of curvature, artifacts are suppressed and the SN ratio of the image is increased. As a result, an effect that an image in the region of interest can be obtained satisfactorily is obtained.

  When the gel member 10 can be replaced as described above, a plurality of gel members having different materials, thicknesses, sizes, positions, etc. of the sheet-like light absorber are prepared and replaced according to the measurement contents. Also good. For example, the thicker the light absorber, the lower the frequency of the generated photoacoustic wave. In this case, since the photoacoustic wave is not easily attenuated, the photoacoustic wave reaches the deep part of the subject, and a deep part can be imaged. On the other hand, the thinner the light absorber, the higher the frequency of the photoacoustic wave. In this case, although the attenuation is easy, the measurement resolution is improved. Therefore, the frequency of the photoacoustic wave can be changed by exchanging the gel member according to the depth and size of the measurement target.

  According to the present embodiment, an ultrasonic image and a photoacoustic image of a subject can be obtained with high definition using a single probe with a simple configuration.

[Modification]
Although the sheet-like light absorber has been described here, a configuration in which a light absorber such as a dot shape or a spherical shape is embedded in the gel member or in the vicinity of the surface thereof may be used. Even in this case, ultrasonic imaging using a photoacoustic wave as a transmission ultrasonic wave can be realized with a simple configuration. At that time, a plurality of light absorbers having different light absorption characteristics may be embedded.

[Embodiment 4]
In the present embodiment, a subject information acquisition apparatus using the hand-held probe 1 shown in the above embodiments will be described with reference to FIG. This apparatus can generate image data inside a subject with two modalities of ultrasonic imaging and photoacoustic imaging. The processing flow in FIG. 3 is actually executed by a subject information acquisition apparatus as in this embodiment.

  The measurement target of the apparatus is a subject 10. The apparatus includes a probe 1, a light source 13, a signal processing unit 14, an information processing unit 15, and a display unit 16. However, the display unit 16 is not always necessary, and the reconstructed image data may be stored in the memory.

  The probe 1 and the light source 13 described above are used. The signal processing unit 14 performs the process in step S304 in FIG. As the signal processing unit 14, an amplifier, an AD converter, various correction circuits, and the like can be used. As the information processing unit 15, an information processing apparatus that includes a CPU, a memory, and the like and operates according to a program or the like, for example, a PC or a workstation is preferable. As the display unit 16, any image display device such as a liquid crystal display or an organic EL display can be used.

  1: probe, 2: gripping part, 3: detection surface, 4: detection element, 7: cover member, 8: light absorber

Claims (17)

A gripping part;
A plurality of detection elements that receive acoustic waves and output electrical signals;
A detection surface on which the plurality of detection elements are arranged;
A light absorber support part in which a light absorber that absorbs light emitted from a light source and generates an acoustic wave is disposed;
A hand-held probe characterized by comprising: The hand-held probe according to claim 1, further comprising an emission end that is disposed on the detection surface and irradiates the light. The light absorber support part is positioned between the subject and the detection surface when the handheld probe is pressed against the subject so that the detection surface faces the subject. The hand-held probe according to claim 1 or 2. The hand-held probe according to claim 3, wherein the detection surface has a concave shape with respect to the subject. The light absorber support part is a film-like member,
The hand-held probe according to claim 1, wherein the light absorber is provided on the film- like member . The hand-held probe according to claim 5, further comprising a coupling agent filled between the light absorber support and the detection surface. The light absorber support part is a bag-shaped member,
The hand-held probe according to any one of claims 1 to 4, wherein the light absorber is provided on the bag- shaped member . The hand-held probe according to claim 7, further comprising a coupling agent filled in the bag-shaped member. The hand-held probe according to claim 5, wherein the light absorber has a dot shape. The hand-held probe according to any one of claims 5 to 9, comprising a plurality of the light absorbers having different light absorption characteristics from each other. The light absorber support part is a film-like member,
The hand-held probe according to claim 2, wherein the light absorber is provided on an optical axis of the film- like member from the emission end. The light absorber support is a gel;
The hand-held probe according to any one of claims 1 to 4, wherein the light absorber is provided inside the gel. The hand-held probe according to claim 12, wherein the light absorber has a sheet shape. The hand-held probe according to claim 13, wherein the sheet-like light absorber has a curvature substantially equal to the detection surface. The handheld probe according to any one of claims 1 to 14, wherein the light absorber support part is detachable from the grip part. The hand-held probe according to any one of claims 1 to 15,
An information processing unit;
Have
The information processing unit uses the electrical signal derived from the acoustic wave propagated from the subject in a state where the handheld probe is pressed against the subject so that the detection surface faces the subject. An object information acquisition apparatus for acquiring characteristic information inside the object. The information processing unit includes the characteristic information using the electrical signal derived from an echo wave reflected from the subject by the acoustic wave generated from the light absorber disposed on the light absorber support unit, and The object information acquiring apparatus according to claim 16, wherein the characteristic information using the electrical signal derived from a photoacoustic wave generated from the inside of the object irradiated with light is acquired.

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